The present invention relates to passive infra-red (PIR) motion detectors of the type used in outdoor lighting fixtures to illuminate an area such as a walkway or driveway when a person or automobile approaches. The invention is more particularly directed to the zonal pattern for covering the monitored field of view.
Outdoor motion-activated lighting fixtures are found in widespread use to monitor and illuminate areas around houses and other buildings such as walkways, driveways, garden areas, gateways and other areas subject to pedestrian traffic. One form of motion-activated fixture includes a floodlight, or frequently a pair of floodlights, and a motion detector housing supported on a common base plate that is mounted to a wall of a building or other structure. The floodlights and motion detector housing are each movably mounted to the base plate so that the lights and the motion detector can each be aimed at a desired target area. See for example U.S. Pat. No. 5,381,323.
The motion detector operates by creating a number of narrow detection zones extending out from the motion detector housing in different directions in the field of view. The detection zones may be envisioned as sensitive fingers stretching out from the motion detector housing into the field of view. See FIGS. 1, 2A and 2B for examples of detection zones. Infra-red energy emanating from a source located within an individual finger-like detection zone is directed onto a sensor in the motion detector housing while infra-red energy from regions between detection zones is not directed to the sensor. The sensor responds only when the infra-red energy impinging upon it changes, and the energy impinging upon the sensor will change whenever a person enters or leaves a detection zone. Thus, the pattern of detection zones determines to a great extent the size and shape of the region monitored by the motion detector and the coarseness or fineness with which the region is monitored.
Known motion detectors provide a number of different detection zone patterns. The zonal patterns generally include a group of detection zones, sometimes called the “far” zones, that is spread out from side to side over some angular width and that looks out to the far reaches of the monitored region. (See for example FIG. 2A.) Some zonal patterns provide coverage at more than one level by defining several groups of detection zones aimed downward by different amounts. The group of far zones is angled downward the least so as to look out at the farthest regions, and one or more other groups of zones are angled downward by greater amounts to look at closer-in regions. Some have so-called wide-angle coverage, meaning that they monitor an area with side-to-side angular spread upwards of 140 degrees.
Recently motion detectors for floodlight fixtures have become available that provide more than 180 degrees of side-to-side coverage. That means the motion detector looks backward to some extent—in effect, it looks over its shoulder—to detect a person approaching from behind. This is useful, for example, when the light fixture is mounted on a wall near a doorway. The motion detector extends out from the wall so that the doorway is set back somewhat behind the motion detector. The motion detector is primarily aimed to monitor the area out in front of the doorway, but with more than 180 degrees of coverage the motion detector can detect a person coming out through the door and turn on the light in response.
In the typical dual-flood fixture the motion detector housing is movably mounted so that it can be aimed up and down and side to side. This enables the housing to be turned so as to improve the coverage of the particular target area for any given installation. When the motion detector housing is tilted only slightly downward, the far zones look out into the distance more to cover a deeper area, thus increasing the range. As the housing is tilted down through a greater angle, the far zones look down more and cover a shorter range. As the motion detector housing is moved, however, the entire zonal pattern is shifted. Aiming the motion detector housing more downward to shorten the forward-looking range will cause any close-in detection zones to be shifted even closer in and will cause any backward-looking zones to be shifted upward to look farther back and possibly even skyward. The result is a compromise in the motion detector's coverage and performance.